IMPACT OF RF POWER AND CURRENT ON RF MEMS SHUNT CAPACITIVE SWITCHES
X. ROTTENBERG, B. NAUWELAERS, W. DE RAEDT, H. A. C. TILMANS

Abstract. This work gives new insights in the problems due to the RF current flowing in the bridge of RF MEMS shunt switching devices subject to a large RF power. A novel description of the current density in the up state of the device is presented. In this model, the peak current density is of the same order of magnitude in both RF-ON and -OFF states. An incident RF power of 1 W in the GHz range leads to RF peak current densities in a 1 µm thick Al MEMS bridge of the order of 10¹⁰ A/m². We used a simplified current model to derive a general expression linking the dissipated power in the bridge to the available RF power and revise the RF-Joule heating problem. We use then the available RF power to drive thermal simulations of the devices. We identify the decisive role of the bridge length in the definition of the maximum temperature in the device. 2 W of RF power produce maximum temperatures below 65^oC in the RF-ON and RF-OFF states provided the bridge length is kept below 300 µm. On bridges longer than 500 µm, the same RF power easily produces temperatures in excess of 100^oC in the RF-ON state. Finally, coupled RF and thermal simulations are realized using the full 3D distribution of RF-Joule heat sources in the device to validate the conclusions from our simplified RF-Joule heating study.